Parkinson's disease affects between 1.0-1.5 million Americans, which is greater than the number of patients diagnosed with multiple sclerosis, muscular dystrophy, and Lou Gehrig's disease combined. Each year, 50,000 American are diagnosed with Parkinson's disease. For some, the motor symptoms of Parkinson's disease are difficult to control even with dopaminergic treatments. Deep Brain Stimulation (DBS) has been applied therapeutically for well over a decade for the treatment of neurological disorders, including Parkinson's Disease, via electrical stimulation of one or more target sites, including the subthalamic nucleus (STN) and internal segment of globus pallidus (GPi). DBS has become a prominent treatment option for many disorders, because it is a safe, reversible alternative to lesioning. For example, DBS is the most frequently performed surgical disorder for the treatment of advanced Parkinson's disease. There have been approximately 30,000 patients world-wide that have undergone DBS surgery.
However, DBS needs a long, complex and invasive surgery to succeed. For example, multiple stimulation leads are typically implanted adjacent the target sites within the brain of the patient. In particular, multiple burr holes are cut through the patient's cranium as not to damage the brain tissue below, a large stereotactic targeting apparatus is mounted to the patient's cranium, and a cannula is scrupulously positioned through each burr hole one at a time towards each target site in the brain. Microelectrode recordings may typically be made to determine if each trajectory passes through the desired part of the brain, and if so, the stimulation leads are then introduced through the cannula, through the burr holes, and along the trajectories into the parenchyma of the brain, such that the electrodes located on the lead are strategically placed at the target sites in the brain of the patient. Disadvantageously, the cutting of multiple burr holes and the introduction of the leads along multiple trajectories into the brain increases trauma and risk to the patient. Additionally, the selection criteria restrict the patient population eligible for DBS to only 1.6-4.5% (see Morgante L., et al, How Many Parkinsonian Patients are Suitable Candidates for Deep Brain Stimulation of Subthalamic Nucleus. Results of a Questionaire, Parkinsonian Related Disorders, 2007; 13:528-531). Further details discussing the treatment of diseases using DBS are disclosed in U.S. Pat. Nos. 6,845,267 and 6,950,707, which are expressly incorporated herein by reference.
There is, thus, a need to develop less invasive efficacious treatments for patients with Parkinson's disease. Spinal Cord Stimulation (SCS) techniques, which is currently used in treating chronic neuropathic pain of the trunk and limbs by directly stimulating spinal cord tissue (e.g., the dorsal column) via one or more leads implanted within the epidural space, is a promising option for patients suffering from Parkinson's disease. It is believed that symptoms of motor disorders, such as Parkinson's disease, may be the result of control issues driven by sensory input. A patient with a motor disorder may have a healthy motor cortex, but the input to the motor cortex may be inappropriate. An imbalance between excitatory and inhibitory input into the motor cortex may result in motor disorder symptoms. Sensory input travels to the motor cortex via sensory nerves in the dorsal column. Thus, in an effort to restore balance between the excitatory and inhibitory inputs into the motor cortex, it is believe that stimulation applied to the dorsal column of the spinal cord in conventional SCS treatments may effectively treat motor disorders. Such dorsal column stimulation for treating symptoms of motor disorders has not yet found widespread use, however, because long-term efficacy in a large number of patients has not been demonstrated.
However, some have reported improvement of motor control using SCS in animal models and in humans. For example, using chronic and advanced Parkinson's disease rodent models, it has been shown that epidural electrical stimulation of the dorsal column was able to restore locomotive ability (see Romulo Fuentes, et al., Restoration of Locomotive Function in Parkinson's Disease by Spinal Cord Stimulation: Mechanistic Approach, Eur J Neurosci, 2010 October; 32(7): 1100-1108). A case study where SCS at the T9-T10 vertebral levels has been shown to alleviate motor Parkinsonian symptoms in the off-drug condition to the same extent as levodopa intake alone (see Fenelon G., Spinal Cord Stimulation for Chronic Pain Improved Motor Function in a Patient with Parkinson's Disease, Parkinsonian and Related Disorders 18 (2012) 213-214). Others have published that SCS can be used to treat movement disorders (see U.S. Patent Publications 2007/0060954, 2010/0023103, and 2012/0330391.
Thus, since SCS is a minimally-invasive approach, SCS techniques for effectively managing symptoms of motor disorders remain attractive in comparison to brain stimulation-based methods, such DBS. In order to achieve an effective result from conventional SCS, the stimulation lead or leads must be placed in a location, such that the delivered stimulation energy creates an electrical field, which when strong enough, depolarizes (or “stimulates”) the neural fibers within the spinal cord beyond a threshold level, thereby inducing the firing of action potentials (APs) that propagate along the neural fibers to provide the desired efficacious therapy to the patient. It is believed that the antidromic activation (i.e., the APs propagate in a direction opposite to their normal direction, which in the case of the spinal cord dorsal column (DC) neural fibers, propagate in the caudal direction) of the large diameter DC neural fibers provides the actual pain relief to the patient by reducing/blocking transmission of smaller diameter pain fibers via interneuronal interaction in the dorsal horn of the spinal cord, while the orthodromic activation (i.e., the APs propagate in their normal direction, which in the case of the spinal cord, propagate in the rostral direction) of the large diameter DC neural fibers generate action potentials that arrive at the thalamus and are relayed to the sensory cortex, thereby creating a side-effect in the form of a sensation known as paresthesia, which can be characterized as a tingling sensation that replaces the pain signals sensed by the patient. The paresthesia induced by the stimulation and perceived by the patient should be located in approximately the same place in the patient's body afflicted by the motor disorder.
Although alternative or artifactual sensations are usually tolerated relative to the sensation of pain, patients sometimes report these sensations to be uncomfortable, and therefore, they can be considered an adverse side-effect to SCS therapy in some cases. There, thus, remains a need to treat movement disorders using SCS therapy while preventing patients from perceiving paresthesia.